A replacement for words containing the prefix, "uni-". Has a more negative connotation than mainstream words such as, unitard, unicycle, uniform, unibrow, and the like. To clarify, in speaking to a friend, the term unibrow is more appropriate; for an enemy, unis is fitting.

(replacement of unibrow)
Girl 1: "OMG look at her new default! She's sporting full facial hair-- a stache, beard, AND unis!"
Girl 2: "WTF I would totes hit up the salon so hard if I had a unis!"

(replacement of unicycle)
Girl: "That man is riding a unis throughout campus! What a toolbag!"

When a person quickly and sharply slaps another person in the forehead, creating one of those classic "what the hell?" moments, which always tend to be fun.
RULES:
1. You MUST say unis when performing a unis on somebody. It is pronounced (yoo-nIS).
2. It is MANDATORY that it be on the forehead. If it is anywhere else on the body, it is null and void.
3. It is IMPERITIVE that it be a slap. Don't punch people in the forehead. You'll look like a complete retard, and it won't count anyways, so it'll just be a big lump of fail.

Dustin: (slaps John on the forehead) UNIS!
Jonathan: Damnit Dustin! What'd I tell you about that?
Kreig: (also slaps John on the forehead) Unis!
Jonathan: SON OF A BITCH!!